1. Field of the Invention
This invention relates to a flash unit having a flash output control device, and more particularly to a flash unit which is capable of indicating whether or not flash output control operation of the flash output control device has been effected.
2. Description of the Prior Art
Automatic flash output control flash units having a flash output control device which receives and meters the flashlight reflected by an object and which stops light emission of the flash unit, that is, effects flash output control, when the quantity of light received has reached a predetermined quantity, have been widely used in recent years. However, with the automatic flash output control flash units of this type, where the object is very distant, even if the flash unit emits its maximum quantity of light, a predetermined quantity of reflected light may not be obtained and the flash output control device may not operate to effect flash output control operation. In such case, a proper exposure is not obtained and, therefore, there have been proposed various flash output control indication devices which indicate to the photographer whether or not flash output control operation has taken place. These flash output control indication devices are generally of two types. One type is a flash output control non-performance indication device which informs the photographer with the aid of a lamp or a buzzer, that flash output control operation has not been effected. The other type is a flash output control performance indication device which informs the photographer likewise that flash output control operation has been effected. However, these indication devices use the battery of the flash unit as their power source and this gives rise to the following problems.
In the flash output control non-performance indication device, when a flash output control operation has not been effected, the flash unit is emitting its maximum possible quantity of light and a large current is being supplied from the battery to a DC-DC converter for charging the main capacitor of the flash unit. Therefore, the terminal voltage of the battery is decreased due to the internal resistance of the battery, so that the lamp or buzzer of the indication device may become inoperative and warning indication of flash output control non-performance may become impossible. Also, in the flash output control performance indication device, when the flash unit has emitted a quantity of light corresponding to its whole quantity of light emission under flash output control operation, a situation similar to that described above occurs and, indication of flash output control performance becomes impossible.